ConfigLang

An embedded configuration and automation language library written in pure C99 with Python bindings. ConfigLang provides a simple, readable syntax for configuration files with support for variables, conditionals, and type safety.

pypi:https://pypi.org/project/configlang/

Features

• Pure C99 - No external dependencies
• Python Bindings - Easy integration with Python projects
• Type System - Integer and string types with type checking
• Const Variables - Immutable configuration values
• Conditionals - If logic for dynamic configuration
• Variable References - Copy values between variables
• Multiline Strings - Support for complex text values
• Comments - Single-line comments with #
• Save/Load - Persist configuration state to files

Language Syntax

Critical Syntax Rules

Important constraints to remember:

1. Variables must be defined before use - You cannot reference a variable in a conditional before it has been declared with set
2. Single statement per if block - Each if block can contain only ONE set statement
3. Closing brace on same line - The } must appear on the same line as the statement inside the if block
4. No else clause - Use chained if statements instead of if-else

Variables

Set integer or string variables:

set x = 10
set name = "Hello World"
set count = 42

Const Variables

Create immutable variables:

const set max_users = 100
const set app_name = "MyApp"

Attempting to modify a const variable will raise an error.

Variable References

Copy values from one variable to another:

set original = 42
set copy = original

set name = "Config"
set backup = name

Conditionals

CORRECT: Basic if statement with closing brace on same line:

set value = 60
if value > 50 { set value = 50 }

CORRECT: Variable must be defined before use in condition:

set debug = 0
set log_level = "info"
if debug == 1 { set log_level = "debug" }

CORRECT: Chained if statements for multiple conditions:

set environment = "production"
set timeout = 30

if environment == "development" { set timeout = 300 }
if environment == "staging" { set timeout = 100 }
if environment == "production" { set timeout = 30 }

CORRECT: Chained if statements (if-if pattern):

set x = 55
if x > 50 { set x = 50 } if x < 10 { set x = 10 }

INCORRECT: Closing brace on separate line:

# This will fail to parse!
if value > 50 { 
    set value = 50
}

INCORRECT: Multiple statements in if block:

# This will fail - only ONE set per if block!
if debug == 1 {
    set verbose = 1
    set trace = 1
}

INCORRECT: Variable used before definition:

# This will fail - x is not defined yet!
if x > 50 { set x = 50 }
set x = 55

Comparison Operators

All standard comparison operators are supported:

• > - Greater than
• < - Less than
• >= - Greater than or equal
• <= - Less than or equal
• == - Equal to
• != - Not equal to

Example:

set x = 10
if x >= 10 { set ready = 1 }
if x != 0 { set active = 1 }

Multiline Strings

For complex text content, use multiline delimiters:

set config = #%%%
line 1
line 2
line 3
%%%#

Comments

Single-line comments start with #:

# This is a comment
set x = 10  # Inline comment

Installation

C Library

Compile the C library:

# Linux/macOS
gcc -shared -fPIC -std=c99 -o libconfiglang.so configlang.c

# macOS (alternative)
gcc -shared -fPIC -std=c99 -o libconfiglang.dylib configlang.c

# Windows
gcc -shared -o configlang.dll configlang.c

Compile the test program:

gcc -std=c99 -o test test.c configlang.c
./test

Python Package

Install from source:

pip install .

Or install in development mode:

pip install -e .

Usage Examples

C API

#include "configlang.h"
#include <stdio.h>

int main(void) {
    // Create instance
    ConfigLang* cfg = cfg_create();
    
    // Load configuration
    const char* code = 
        "set port = 8080\n"
        "set host = \"localhost\"\n"
        "const set max_connections = 100\n"
        "if port < 1024 { set port = 8080 }\n";
    
    int result = cfg_load_string(cfg, code);
    if (result != ERR_CFG_OK) {
        fprintf(stderr, "Error: %s\n", cfg_get_error(cfg));
        cfg_destroy(cfg);
        return 1;
    }
    
    // Get values
    int port;
    const char* host;
    
    cfg_get_int(cfg, "port", &port);
    cfg_get_string(cfg, "host", &host);
    
    printf("Server: %s:%d\n", host, port);
    
    // Modify value
    cfg_set_int(cfg, "port", 9000);
    
    // Save configuration
    cfg_save_file(cfg, "server.cfg");
    
    // Cleanup
    cfg_destroy(cfg);
    
    return 0;
}

Python API

from configlang import ConfigLang

# Create instance
cfg = ConfigLang()

# Load configuration
code = """
set debug = 0
set port = 8080
set host = "localhost"
const set max_connections = 100
if debug == 1 { set port = 3000 }
"""

cfg.load_string(code)

# Get values
print(f"Port: {cfg.get_int('port')}")
print(f"Host: {cfg.get_string('host')}")

# Modify value
cfg.set_int('port', 9000)

# Dictionary-style access
cfg['port'] = 3000
print(f"Port: {cfg['port']}")

# Save configuration
cfg.save_file('server.cfg')

Context Manager (Python)

with ConfigLang() as cfg:
    cfg.load_string('set x = 10\nset name = "Test"')
    print(cfg.get_int('x'))
    # Automatically cleaned up

API Reference

C Functions

Function	Description
cfg_create()	Create a new ConfigLang instance
cfg_destroy(cfg)	Destroy instance and free resources
cfg_load_file(cfg, path)	Load configuration from file
cfg_load_string(cfg, code)	Load configuration from string
cfg_get_int(cfg, name, out)	Get integer variable value
cfg_get_string(cfg, name, out)	Get string variable value
cfg_set_int(cfg, name, value)	Set integer variable value
cfg_save_file(cfg, path)	Save configuration to file
cfg_get_error(cfg)	Get last error message

Python Methods

Method	Description
ConfigLang()	Create new instance
load_file(path)	Load configuration from file
load_string(code)	Load configuration from string
get_int(name)	Get integer variable value
get_string(name)	Get string variable value
set_int(name, value)	Set integer variable value
save_file(path)	Save configuration to file
get_error()	Get last error message
get(name)	Auto-detect type and get value

Error Codes

Code	Constant	Description
0	ERR_CFG_OK	Success
1	ERR_CFG_PARSE_ERROR	Syntax error in configuration
2	ERR_CFG_FILE_ERROR	File I/O error
3	ERR_CFG_VARIABLE_NOT_FOUND	Variable doesn't exist
4	ERR_CFG_CONST_VIOLATION	Attempted to modify const variable
5	ERR_CFG_TYPE_MISMATCH	Variable type mismatch
6	ERR_CFG_NULL_POINTER	NULL pointer passed
7	ERR_CFG_OUT_OF_MEMORY	Memory allocation failed

Python Exceptions

• ConfigLangError - Base exception class
• ParseError - Syntax error in configuration
• VariableNotFoundError - Variable doesn't exist
• ConstViolationError - Attempted to modify const variable
• TypeMismatchError - Variable type mismatch

Example Configuration File

# Application Configuration
const set app_name = "MyApplication"
const set version = "1.0.0"

# Server Settings
set debug = 0
set host = "0.0.0.0"
set port = 8080

# Apply production settings
if debug == 0 { set port = 80 }
if debug == 0 { set workers = 4 }

# Apply development settings
if debug == 1 { set port = 8080 }
if debug == 1 { set workers = 1 }

# Database Configuration
set db_host = "localhost"
set db_port = 5432
set db_name = "myapp"

# Limits
const set max_connections = 100
const set timeout = 30

# Multiline description
set description = #%%%
This is a multi-line
application description
that spans several lines.
%%%#

Complete Working Example

This example demonstrates all features with correct syntax:

# ============================================
# Complete ConfigLang Example
# ============================================

# Constants (immutable)
const set APP_NAME = "WebServer"
const set VERSION = "2.0.0"
const set MAX_USERS = 1000

# Environment variable
set environment = "production"

# Default values
set port = 8080
set host = "localhost"
set workers = 2
set timeout = 30
set log_level = "info"

# Production configuration
if environment == "production" { set port = 80 }
if environment == "production" { set host = "0.0.0.0" }
if environment == "production" { set workers = 8 }
if environment == "production" { set log_level = "warning" }

# Development configuration  
if environment == "development" { set port = 3000 }
if environment == "development" { set host = "127.0.0.1" }
if environment == "development" { set workers = 1 }
if environment == "development" { set log_level = "debug" }

# Staging configuration
if environment == "staging" { set port = 8080 }
if environment == "staging" { set workers = 4 }

# Database settings
set db_enabled = 1
set db_host = "localhost"
set db_port = 5432

if db_enabled == 1 { set db_name = "production_db" }
if db_enabled == 0 { set db_name = "test_db" }

# Feature flags
set feature_cache = 1
set feature_logging = 1

if feature_cache == 1 { set cache_size = 1024 }
if feature_logging == 1 { set log_size = 100 }

# Variable references
set backup_host = host
set backup_port = port

# Multiline content
set welcome = #%%%
=========================================
  Welcome to WebServer v2.0.0
  Environment: production
  Running on: 0.0.0.0:80
=========================================
%%%#

Language Grammar

program      → statement*
statement    → comment | set_stmt | if_stmt
comment      → '#' text '\n'
set_stmt     → 'const'? 'set' identifier '=' value
if_stmt      → 'if' condition '{' set_stmt '}' if_stmt?
condition    → identifier operator value
operator     → '>' | '<' | '>=' | '<=' | '==' | '!='
value        → integer | string | identifier | multiline
integer      → '-'? [0-9]+
string       → '"' [^"]* '"'
multiline    → '#%%%' .* '%%%#'
identifier   → [a-zA-Z_][a-zA-Z0-9_]*

Key Grammar Notes:

• if_stmt can only contain ONE set_stmt inside the braces
• The closing } must be on the same line as the set_stmt
• Chaining is done by following one if_stmt with another if_stmt
• There is no separate else keyword - use chained if statements

Type System

ConfigLang has a simple type system with two types:

1. Integer - Signed integers (e.g., 42, -10, 0)
2. String - Text values (e.g., "Hello", "Config")

Types are checked at runtime. Attempting to get or set a variable with the wrong type will result in a TYPE_MISMATCH error.

Implementation Limits

The C implementation defines these limits (configurable in source):

• MAX_VARIABLES - 128 variables maximum
• MAX_VAR_NAME - 32 characters for variable names
• MAX_STRING_VALUE - 1024 characters for string values
• MAX_LINE_LENGTH - 2048 characters per line
• MAX_ERROR_MSG - 256 characters for error messages

Limitations

• No floating-point numbers (integers only)
• No arithmetic operations (use for configuration, not computation)
• No loops (conditionals only)
• No functions or procedures
• No arrays or complex data structures
• String operations are limited to assignment
• Only one set statement per if block
• No else keyword - use chained if statements instead
• Closing brace must be on same line as the statement
• Variables must be declared before use in conditionals

Use Cases

ConfigLang is designed for:

• Application configuration files
• Build system configuration
• Environment-specific settings
• Feature flags and toggles
• Embedded system configuration
• Game settings and preferences
• Simple automation scripts

Best Practices

1. Define variables before conditionals: Always declare variables with set before using them in if conditions
2. Use chained if statements: Instead of if-else, use multiple if statements
3. Keep conditionals simple: Each if block should modify only one variable
4. Use const for fixed values: Mark configuration values that shouldn't change as const
5. Group related settings: Use comments to organize your configuration into logical sections
6. One line per if block: Keep the syntax compact with if condition { set var = value }

Common Patterns

Environment-Based Configuration

set env = "production"
set port = 80

if env == "development" { set port = 3000 }
if env == "staging" { set port = 8080 }
if env == "production" { set port = 80 }

Feature Flags

set feature_x = 1
set feature_y = 0

set module_x_enabled = 0
set module_y_enabled = 0

if feature_x == 1 { set module_x_enabled = 1 }
if feature_y == 1 { set module_y_enabled = 1 }

Conditional Defaults

set mode = 1
set timeout = 30

if mode == 0 { set timeout = 10 }
if mode == 1 { set timeout = 30 }
if mode == 2 { set timeout = 60 }

License

MIT License - See LICENSE file for details

Author

hejhdiss

Links

• GitHub: https://github.com/hejhdiss/configlang
• Issues: https://github.com/hejhdiss/configlang/issues

Contributing

Contributions are welcome! Please feel free to submit pull requests or open issues for bugs and feature requests.

Changelog

Version 1.0.0

• Initial release
• C library implementation
• Python bindings
• Full test suite
• Documentation